Optimizing the electrodeposition of multinary compounds is of key importance for tomorrow technologies. Cu-In-Se system represents a case example, with a great potential in the field of photovoltaics. At IRDEP we achieved efficiencies up to 11.5% based on electrodeposited Cu-In-Se material.

The electrochemical deposition of this ternary compound, whose components exhibit very different redox potentials and several oxidation states, is a complex process.

In the present work, the electrocrystallization mechanism of CuInSe₂ is investigated, in dilute acidic solutions, by polarization and impedance spectroscopy using a rotating disc electrode. The bulk composition is determined by x-ray fluorescence. The morphology is characterized by SEM and the structure by X-ray diffraction.

At low polarizations, no indium is deposited, binary Cu-Se phases are obtained. These phases catalyse the reduction of Se(IV) species into elemental selenium, which, in turn, enables the incorporation of indium beyond a potential threshold close to –0.6V/MSE. At higher overpotentials, CuInSe₂ chalcopyrite phase is formed, together with elemental selenium and additional Cu_xSe phases. In the intermediate potential zone corresponding to indium incorporation, the polarization curve exhibits a current peak similar to a passivation process. A specific impedance response with a large capacitive feature with a negative polarization resistance is observed. This indicates the adsorption of a blocking, poorly conducting compound.

A reaction path is proposed which accounts for the main experimental features. This leads to a better understanding of key parameters controlling the composition and the structure of the layers. The proportion between different phases and their organization at the nanoscale in the film are governing the recrystallization processes during post-thermal annealing and finally the photovoltaic properties.

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